Plato's Myth of Er greatly influenced subsequent religious and philosophical thought, up to and including our very idea of heaven and hell.
Er was slain in battle but came back to life 12 days later to tell the living of that which he had seen. During these 12 days, his soul went on a journey to a meadow with four openings, two into the heavens above and two into the earth below.
Judges sat in this meadow and ordered the good souls up through one of the openings into the heavens and the bad ones down through one of the openings into the earth. Meanwhile, clean and bright souls floated down to the meadow from the other opening into the heavens, and dusty and worn out souls rose up to the meadow from the other opening into the earth.
Each soul had returned from a thousand year journey, but whereas the clean and bright souls spoke merrily of that which they had enjoyed in the heavens, the dusty and worn out souls wept at that which they had endured in the underground. Souls that had committed heinous crimes, such as those of tyrants or murderers, were not permitted to rise up into the meadow, and were condemned to an eternity in the underground.
After seven days in the meadow, the souls travelled for five more days to the spindle of Necessity, a shaft of intensely bright light that extends into the heavens and that holds together the universe. The souls were then asked to come forth one by one and to choose their next life from a scattered jigsaw of human and animal lives. Not having known the terrors of the underworld, the first soul hastily chose the life of a powerful dictator, only to discover that he was fated, among many other evils, to devour his own children. Although he had been virtuous in his previous life, his virtue had arisen out of habit rather than out of philosophy, and so his judgement was poor. In contrast, the souls that had known the terrors of the underworld often chose a better, more virtuous life, but this they did on no other basis than harsh experience. Thus, many of the souls exchanged a good destiny for an evil or an evil for a good, and so on for all eternity. The soul of the wily Odysseus, which was the last to come forth, sought out the life of a private man with no cares. This he found easily, lying about and neglected by everyone else.